TY - JOUR T1 - Agonist-, Antagonist-, and Benzodiazepine-Induced Structural Changes in the α<sub>1</sub> Met<sup>113</sup>-Leu<sup>132</sup> Region of the GABA<sub>A</sub> Receptor JF - Molecular Pharmacology JO - Mol Pharmacol SP - 483 LP - 493 DO - 10.1124/mol.106.028662 VL - 71 IS - 2 AU - Jessica Holden Kloda AU - Cynthia Czajkowski Y1 - 2007/02/01 UR - http://molpharm.aspetjournals.org/content/71/2/483.abstract N2 - The structural basis by which agonists, antagonists, and allosteric modulators exert their distinct actions on ligand-gated ion channels is poorly understood. We used the substituted cysteine accessibility method to probe the structure of the GABAA receptor in the presence of ligands that elicit different pharmacological effects. Residues in the α1 Met113-Leu132 region of the GABA binding site were individually mutated to cysteine and expressed with wild-type β2 and γ2 subunits in Xenopus laevis oocytes. Using electrophysiology, we determined the rates of reaction of N-biotinaminoethyl methaneth-iosulfonate (MTSEA-biotin) with the introduced cysteines in the resting (unliganded) state and compared them with rates determined in the presence of GABA (agonist), 4-[6-imino-3-(4-methoxyphenyl)pyridazin-1-yl]butanoic acid hydrobromide (SR-95531; antagonist), pentobarbital (allosteric modulator), and flurazepam (allosteric modulator). α1N115C, α1L117C, α1T129C, and α1R131C are predicted to line the GABA binding pocket because MTSEA-biotin modification of these residues decreased the amount of current elicited by GABA, and the rates/extents of modification were decreased both by GABA and SR-95531. Reaction rates of some substituted cysteines were different depending on the ligand, indicating that barbiturate- and GABA-induced channel gating, antagonist binding, and benzodiazepine modulation induce specific structural rearrangements. Chemical reactivity of α1E122C was decreased by either GABA or pentobarbital but was unaltered by SR-95531 binding, whereas α1L127C reactivity was decreased by agonist and antagonist binding but not affected by pentobarbital. Furthermore, α1E122C, α1L127C, and α1R131C changed accessibility in response to flurazepam, providing structural evidence that residues in and near the GABA binding site move in response to benzodiazepine modulation. The American Society for Pharmacology and Experimental Therapeutics ER -